1. Field of the Invention
The invention is concerned with a circuit arrangement for the triggering of motors, for example those used in digital or analog tape recording devices.
2. Description of Art
In motors for precision drives in which, apart from the exact observation of given speed values, some relevance also lies in rapid speed changes and adoption of changed speed values, it is known to connect the inputs (influences) of the winding arrangement to electricity sources by means of a commutation facility in order to make the rotor follow a given alternating field and to monitor the speed by feedback. Due to the mass driven, the desired reaction of the rotor is not without inertia, but subject to a more or less strong delay.
If the rotor is to adopt a higher speed the delay can be minimized in that, by triggering accordingly, a high turning moment with positive direction is applied to the rotor which is maintained until it is recognized by the feedback that the desired speed is reached and then the triggering is reduced again to the stationary turning moment with positive direction which is necessary to maintain the speed. A modification of speed towards a smaller value can easily be achieved particularly in that the stationary triggering is switched off, then an opposite turning moment, i.e. in the negative direction, is generated and, after the lowered speed is reached, the stationary triggering is reestablished. It is a problem in this method that the speed reached after decay of the negatively directed turning moment is not always absolutely identical with the desired speed, thereby making an additional process of deceleration or acceleration necessary. In addition, the commutation sequence of the connections of the winding arrangement has to be synchronized again with the present rotation of the rotor.
Motor speed is controlled during generation of the accelerating field through a control circuit utilizing a tachometer generator and a phase locked loop (PLL) arrangement. However, changing speeds, e.g. from acceleration to deceleration, interrupts the phase locked loop and interferes with the ability of the phase locked loop to remain synchronized. It would therefore be desirable to maintain the phase control loop for the accelerating field in continuous operation even during generation of the decelerating field, when the turning moment in the negative direction is impressed. The problem here is, however, that the triggering facilities in their opposing effects on the rotor obstruct or even destroy each other and thus interrupt the phase locked loop.